Decision Fatigue Calculator — Find Your Decision-Quality Crash Hour

What This Calculator Does

The Decision Fatigue Calculator finds your decision-quality crash hour. Drop your daily conscious decision count, the trivial-vs-meaningful split, scheduled-routine percentage, mental-rest blocks, weekly alcohol intake, and 7-day average sleep. The calculator computes effective decisions after routine compression, layers in rest recovery + alcohol + sleep penalties, and surfaces the specific hour your decision quality measurably degrades — calibrated against Bargh & Vohs / Vohs & Heatherton glucose- willpower research and the Levav & Avnaim-Pesso parole-board study (decisions late afternoon are measurably worse than decisions before lunch).

Most productivity literature treats “willpower” as a vague resource. The decision-fatigue research community has a more specific framing: conscious decisions cost glucose + executive function, and quality measurably degrades after the 70th decision. Famous examples: judges grant parole at 65% pre-lunch and 0% late afternoon; supermarket shoppers buy more impulse items at the end of long shopping trips; founder ego-depletion shows up as terse Slack replies and impulse hires after 5 PM. The calculator surfaces your specific exposure to this pattern.

The Math — Effective Decisions vs Ceiling

Effective decisions accounts for routine-ization — pre-deciding 30% of your day reduces effective load by 15%. Steve Jobs / Obama / Zuckerberg approach (uniform + standing meals + calendared work blocks) isn’t aesthetic theatre; it’s decision-load engineering. Each pre-decision eliminates a conscious-decision slot for higher-stakes choices later in the day. Mental- rest blocks (walks without phone, 10-min meditation, naps) add reclaim — each one restores ~8 effective decisions of capacity.

Penalties capture next-day effects. Alcohol (Walker / Huberman work) fragments REM sleep architecture, degrading next-day executive function and decision quality. The penalty applies to the day after you drink, not the day of. Sleep penalty operates directly: each hour below 7 hrs adds 12 effective- decision penalty because sleep-deprived decisions are measurably worse across multiple replicated studies. Both penalties layer onto the effective-decisions count to produce net fatigue, which drives the crash-hour estimate.

Worked Example — 90 Decisions/Day, 30% Routine

Plug calculator’s defaults: 90 conscious decisions/day, 70% trivial split, 30% routine, 1 rest block, 4 drinks/wk, 7 hrs sleep. Effective decisions = 90 × (1 - 0.5 × 0.30) = 90 × 0.85 = 76.5. Rest recovery = 1 × 8 = 8. Alcohol penalty = (4/7) × 5 = 2.86. Sleep penalty = max(0, 7-7) × 12 = 0. Net fatigue = 76.5 - 8 + 2.86 + 0 = 71.4. Crash hour at netFatigue 71 = 2 PM. Tone = info (51-80 range).

Now bump routine to 60% (Steve Jobs mode): effective = 90 × (1 - 0.5 × 0.60) = 90 × 0.70 = 63. Net fatigue = 63 - 8 + 2.86 = 57.86. Crash hour shifts to 4 PM (sustained quality through more of the workday). Same 90 decisions, very different decision capacity, just because you compressed 30 trivial choices into routine. That’s the math behind “wear the same outfit” — it reclaims an actual hour of peak decision quality on the back end of the day.

The Crash Hour — When To Schedule What

Decision-quality crash isn’t literal — you don’t go from 100% to 0% at exactly 2 PM. The crash hour is where measurable degradation accelerates, from gradual drift to noticeable impairment. Below it, you’re in your peak window. Above it, you’re making decisions you’d reverse the next morning. The practical implication: schedule highest-stakes irreversible decisions BEFORE the crash hour. Hiring decisions, expensive purchases, important relationship conversations, strategic pivots — these belong in your peak window.

The reverse principle: trivial decisions belong in the crash window. Lunch ordering, what to wear tomorrow, which Netflix show — these don’t need decision quality, so spending the depleted late-afternoon hours on them is fine. The mistake most knowledge workers make is the inverse: handling email + Slack at 9 AM (peak quality) and pushing strategic decisions to 5 PM (crash window). Calculator surfaces the crash hour so you can deliberately invert this pattern.

Common Mistakes

Counting only “big” decisions. Bargh & Vohs research counts conscious decisions — which lunch, which email to reply to, which meeting invite to accept, which Slack thread to engage. Even trivial decisions cost glucose. The 90 number isn’t 90 strategic decisions; it’s 90 conscious- attention units allocated. Most people honestly land at 80-120 if they count truthfully.

Coffee as the fix.Caffeine + glucose temporarily mask decision degradation but don’t eliminate it. The 4 PM coffee that “gets you through” borrows against tomorrow’s sleep budget (caffeine half-life is 6 hrs; 4 PM coffee impairs that night’s sleep, increasing tomorrow’s decision-fatigue baseline). Net effect over 7 days is roughly zero — you’re shifting fatigue, not eliminating it.

Treating “productive” breaks as rest blocks.Catching up on email isn’t rest. Listening to a podcast while walking isn’t rest. Scrolling social media isn’t rest. True mental rest = deliberately phone-free, low-stimulus, ≥10 min. Walks without phone (highest research-backed for cognitive recovery). 10-min seated meditation. Short naps. The calc’s 8-effective-decisions-per- rest-block reclaim assumes true rest, not productive breaks disguised as rest.

Underestimating alcohol penalty. The penalty applies to the next day, not the day of. 4 units/wk averaged = 0.57 unit/day = ~3 effective- decision penalty next day. Heavy weekend drinking compounds — the Monday-Tuesday next-day effect is real. Walker / Huberman work shows even 1-2 drinks 3 hrs before bed measurably fragments REM sleep.

Skipping the routine input because it sounds rigid.Routine-ization isn’t about being boring — it’s about reserving conscious decision capacity for choices that matter. 60% routine isn’t 60% of your day on autopilot; it’s 60% of decisions pre-made so the 40% remaining have access to your peak quality. Most high-output knowledge workers run 50-70% routine without recognizing it.

Related Calculators

Pair this with the Cognitive Load Calculator — decision fatigue is one input into the broader cognitive-load score. If your decision fatigue is high but your overall cognitive load is moderate, the right reclaim is decision-routine-ization. If both are high, the issue is structural and needs a bigger reset. The Sleep Debt Calculator is the highest-leverage input — adding 1 hr sleep recovers 12 effective decisions/day, more than any other lever in this calc. The Time Wealth Calculator reframes the question — degraded decisions cost you money (impulse purchases), relationships (terse replies), and momentum (avoidance). And the Deep Work ROI Calculator shows the dollar value of preserved deep-work hours that pre-decided routines + protected morning slots unlock.

How to Read the Result

The crash hour is the one number to act on — any decision after that hour is materially worse than one before lunch. Move high-stakes decisions (hiring, pricing, important emails, financial moves) to mornings; leave the evening for execution on already-decided plans.

• Crash hour before 2pm. Sleep is broken. Two-week reset to 7+ hrs and the crash hour usually slides to 4-6pm. Most other interventions are downstream of this one.
• Crash hour 2-4pm AND meaningful decisions dominate.Apply Obama’s rule — eliminate trivial decisions. Capsule wardrobe, weekly meal plan, breakfast routine free up the morning capacity.
• Crash hour 5pm+.Healthy capacity. Don’t micro-optimize — protect what you have. Schedule the recurring 4pm decision-meeting somewhere else.
• Alcohol penalty is the dominant degrader. Even modest weekly intake (5+ drinks) shifts the crash hour forward by 60-90 min. Three-week dry stretch isolates the effect honestly.